Chemical state modulation of tungsten via highly electronegative nonmetallic elements for enhanced electrochemical energy storage

Abstract

Tungsten (W, 5d⁴6s²), a transition metal, readily provides valence electrons during chemical reactions. Leveraging this property, this work employs a one-step hydrothermal method to introduce the strongly electronegative nonmetals oxygen (O) and selenium (Se) onto an oxidized carbon cloth (OCC) substrate, resulting in the fabrication of the W₁₈O₄₉/OCC and WSe₂/OCC electrode materials, respectively. Material characterization and electrochemical performance analyses indicate that Se performs better in optimizing the chemical states of W, which exhibits the characteristics of coexisting multiple valence states (W⁴⁺, W⁵⁺, and W⁶⁺). This enhances the favorable sites for electron migration in subsequent electrochemical reactions, thereby improving the electrochemical performance of WSe₂/OCC. Kinetic calculations reveal that the energy storage process of WSe₂/OCC features both capacitive and diffusion control. Compared with W₁₈O₄₉/OCC, WSe₂/OCC maintains a certain level of capacitive control during electrochemical reactions while allowing electrons at the liquid–solid interface and the near-surface to migrate to the bulk more easily via diffusion. This activation of internal redox reactions results in a commendable performance by WSe₂/OCC across a series of electrochemical tests (352.1 F g⁻¹ at 1 A g⁻¹). Furthermore, WSe₂/OCC exhibits excellent cycling stability, retaining 100% of its initial capacitance after 10 000 cycles at 10 A g⁻¹, along with remarkable bending resistance.